Method of making paper containers greaseproof



Patented Mar. 6, 1951 METHOD OF MAKING PAPER CONTAINERS GREASEPROOFRalph H. McKee, New York, N. Y.

No Drawing. Application November 17, 1944, Serial No. 563,995

Claims. (01. 226-19) The invention relates to paper containers andparticularly to flexible paper containers adapted to be used for thepackaging and retailing of oils, lubricants, turpentine, kerosene,gasoline, and similar liquid hydrocarbons. The invention also relatestomethods for the manufacture of these containers which hereafter willbe termed grease-proof containers.

Paper, as a manufacturing material for containers, has in recent yearsrapidly gained in importance.

The manufacture of parafilne coated paper containers for the retailingof milk clearly characterizes this development. Parafiine coated papercontainers are for obvious reasons not usable for the commercialhandling and the transportation of oils, lubricants, turpentine andsimilar non-aqueous liquids.

In the past wooden containers and barrels have been frequently used forthese purposes after being coated with a glue solution at an elevatedtemperature, which coating would be dried before the containers wereused.

This proofing method cannot be applied to paper containers which as suchdo not possess suflicient rigidity and stability to withstanddeformation; the brittle glue coating is bound to crack and to burst, ifthe paper container is subjected to the inevitable bending stressesoccurring during the use and transportation, whereby leakage of thecontents will result.

The wooden barrels are nowadays being replaced by steel drums, whichhowever have the great disadvantage that they cannot be discarded atwill and have to be stored for return to the delivery firms.

The solution of the problem which underlies this invention is aggravatedby the necessity to' effect from the applied coating an evaporation ofthe water through the paper walls up to a point where equilibrium isattained with the humidity of the surrounding atmosphere.

It is, therefore, the primary object of the invention to produce acoating for paper containers which renders the safe packaging andretailing of oils, lubricants, turpentine, kerosene, gasoline andsimilar liquid hydrocarbons possible.

It is a further object of the invention to produce a flexiblegrease-proof paper container which will remainunhurtand from which thecoating will not crack or burst off when the container is subjected toinevitable rough handling and resulting bending and impact stresses.

It is another object of the inventionto manufacture an inexpensiveflexible, grease-proof 2 paper container which can be discarded andburned after use.

It is also an object of the invention to produce a paper containerhaving a grease-proof coating which for a certain period after theapplication of the coating preserves sumcient gas porosity to permitthrough its walls the establishment ofa humidity equilibrium between thecoating and the surrounding atmosphere.

It is a further object of the invention to devise a grease proof papercontainer which may be manufactured without difilculty and without orwith but minor changes of the working appliances in existing automaticpaper container manufacturing and filling installations.

It is a further object of the invention to manufacture grease proofflexible paper containers where an aqueous grease proofing liquid isused for the production of the coating and the drying of the coatings iseffected through the container walls and not from the free surface ofthe coating.

It is also an object of the invention to produce grease proof flexiblepaper containers where the grease proofing liquid is applied to thecontainer walls at an elevated temperature and the coating is jellied bychilling under avoidance of drying.

It is a further object of the invention to produce grease proof papercontainers where the solidification of the applied coating is effectedby contact with the cold container filling and the container is sealedbefore the drying of the coating is completed.

It is also an object of the invention to manufacture grease proof papercontainers which can be heatand pressure-sealed at the top and where thesealing will be effected after time of filling or after the containerhas been allowed to stand.

With these objects in view the invention is based on the discovery thatpaper containers can be effectively grease-proofed if a coating isapplied to the same which contains a plasticizer in admixture to a gluesolution.

Multi-wall paper containers have been rendered grease-proof by eitherlacquering the same inside or outside or by inserting an oil insolubleadhesive between the multiple paper sheets in order to unite the sameand hold them together.

The invention does not relate to multi-sheet containers, but to papercontainers which after being coated retain sufiicient porosity topermit, by water evaporation through the wall, the, establishmentof ahumidity equilibrium between the coating and the surrounding atmosphere.

A conditioner may be preferably added to the plasticizer containing aglue solution; if a conditioner is used which is adapted to function asa plasticizer, the latter may be entirely replaced by the conditioner.

Glycerine i preferably used as a plasticizer, but other substances whichare compatible with glue Jellies, such as ethylene glycol, treacle,glucose, may be employed as plasticizers for the purposes of theinvention.

The conditioner ma be taken from the hexahydric alcohols carrying, forinstance, 80% or more polyhydric alcohol; the commercial sorbitol syrupshave been found to be of excellent service; however, other substances,such as for instance butylene glycol, iditol or erythritol may besuccessfully employed as conditioners for the control of the residualmoisture in the coating and to impart thereto increased mechanicalstrength and flexibility.

The glycerine used as a plasticizer should be free from common salt;indeed almost any distilled glycerine having a concentration of 80% ormore will serve.

Glues which will yield a olution of low viscosity are preferred formaking the instant grease proofing liquid.

An example of a usable glue would be a low grade hide glue which by thestandard test of the National Association of Glue Manufacturers wouldshow a jelly strength of 135 grams on the Bloom jellometer.

The presence of a bactericide and of a fungicide is desirable; forinstance, zinc sulfate equal to about one percent of the glue may bepreferably used.

In accordance with a preferred embodiment of the invention a smallpercentage of hexamethylenetetramine, for instance one fourth of 1% ofthe dry weight of the glue may be added.

The acidity of the paper used for the manufacture of the containers willin contact with the applied coating react with the hexamethylenetetramine setting formaldehyde free and thereby producing a tanning ofthe glue, that is, insolubilize the coating and thereby render it waterL, resistant in the course of a few days. Paper will have a pH below 6when made with ordinary rosin-alum size customarily used in the makingof paper. This paper may well be used for the purposes of the invention.

A container or package made of originally porous paper after beinggrease-proofed in the presence of hexamethylenetetramine according tothe invention will be fully impervious to rainfall.

The ranges of the individual components form ing the grease proofingcoating of this invention may vary considerably and lie, for instance,between to 30 parts by weight of glue, 18 to 60 parts by weight of aplasticizer or a mixture of a plasticizer and a conditioner or of aconditioner only if the latter acts asa plasticizer, and 15 to 40 partsby weight of water.

The composition of the coating is given below:

Glue, 5 to 30 parts by weight Plasticizer, to 35 part by weightConditioner, 8 to 25 parts by weight Hexamethylenetetramine, /6 to percent of the glue Water, to 40 parts by weight The amounts of water, ofconditioner, plasticizer used will be chosen depending on the Jellystrength of the glue used, 1. e. a high grade glue requires more waterand conditioner, etc., to give the desired viscosity of the coatingsolution at a given temperature, for instance 150 '1. Likewise, avariation in composition is possible according to whether a thick or athin coating or a change of physical properties is desired.

As a preferred example the grease proofing composition forming thisinvention may be con-.

stituted, as follows:

Glue Bloom strength), 10 parts by weight Glycerine, 18 parts by weightSorbitol syrup, 12 parts'by weight Hexamethylenetetramine, .03 parts byweight Water, 20 parts by weight tion and humidity exchange takes placebetween the drying coating and the surrounding atmosphere, untilequilibrium is reached.

The drying has, therefore, been effected through the container wall, butnot from the free surface of the coating.

The instant method of rendering a paper container grease proof andcapable of holding oils, lubricants, turpentine, gasoline and similarhydrocarbons is particularly adapted to be used with existent automaticpaper container manufacturing and filling installations.

I claim:

1. In a method of grease-proofing containers to be used for thetransport of liquid hydrocarbons, such as gasoline, oils, lubricants andconsisting of a single-layer porous paper having a pH of less than 6,the steps of applying to the inside wall of the containers a coating ofan aqueous solution of a low viscosity glue and of a quantity ofhexamethylene tetramine equal to about 0.2 to 0.5 per cent of the dryweight of the glue hereupon directly filling the container with theliquid hydrocarbon of a sufficiently low temperature to thereby congealthe coating and sealing the same whereupon the coating is hardened bythe formaldehyde set free from the hexamethylene tetramine by contactwith the acid in the container wall and dried by cooperation of itsmoisture content through the porous container wall.

2. In a method of grease-proofing containers to be used for thetransport of liquid hydrocarbons, such as gasoline, oils, lubricants andconsisting of a single-layer porous paper having a pH of less than 6,the steps of applying to the inside wall of the containers a coating ofan aqueous solution heated to about F. of a low viscosity glue and of aquantity of hexamethylene tetramine equal to about 0.2 to 0.5 per centofthe dry weight of the glue hereupon directly filling the containerwith the liquid hydrocarbon coated to about 40 to 50 F., therebycongealing the coating and sealing the same whereupon the coating ishardened by the formaldehyde set free from the hexamethylene tetramineby contact with the acid in the container wall and dried by evaporationof its moisture contents through the porous container wall.

3. In a method of grease-proofing containers to be used for thetransport of cold liquid hydrocarbons, such as gasoline, oils,lubricants and consisting of a single-layer porous paper having a pH ofless than 6, the steps of applying to the inside wall of the containersa heated coating of an aqueous solution of a low viscosity glue,glycerin and sorbitol syrup and of a quantity oi hexamethylene tetramineequal to about 0.2 to 0.5 per cent sisting of a single-layer porouspaper having a pH of less than 6, the steps of applying to the insidewall of the containers a coating of a heated aqueous solution containingin about 20 parts by weight of water about 10 parts by weight of a lowviscosity glue, about 18 parts by weight 01 81.7 erine, about 12 partsby weight of sorbital syrup, about 0.03 parts by weight of hexamethylenetetramine, hereupon directly filling the container with the cold liquidhydrocarbon, thereby congealing the coating and sealing the samewhereupon the coating is hardenedby the formaldehyde set free from thehexamethylene tetramine by contact with the acid in the container walland dried by evaporation of its moisture content through the porouscontainer wall.

5. In a method 01' grease-proofing containers to be used for thetransport of cold liquid hydroauaaoo 6. carbons, such as gasoline, oils,lubricants and consisting of a single-layer porous paper having a pH 01'less than 6, the steps of app ying to the inside wall of the containersa coating of an aqueous solution containing in 15 to 40 parts by weightof water, 5 to parts by weight of a low viscosity glue, 10 to parts byweight of glycerin, '25 to 28 parts by weight of sorbitol syrup, 0.03parts by weight of hexamethylene tetr, hereupon directly filling thecontainer with the cold liquid hydrocarbon, thereby congealing thecoating and sealing the same whereupon the coating is hardened by theformaldehyde set free from the hexamethylene tetramine by contact withthe acid in the container wall and dried by evaporation of its moisturecontent through the porous container wall.

RALPH H. Mc

' REFERENCES CITED The following references are of record in the file orthis patent:

UNITED STATES PATENTS Number Name Date 1,192,765 Durkee July 25, 19161,417,708 Wright May 30, 1922 2,164,494 Brown July 4, 1939 2,164,495Brown July 4 1939 2,414,274 Sass et al. Jan. 14, 1947 FOREIGN PATENTSNumber Country Date 495,352 Great Britain Nov. 11, 1938 OTHER REFERENCESCondensed Chemical Dictionary, 3rd edition, p. 687, Reinhold PublishingCo., 1942. (Copy in Div. 64.)

1. IN A METHOD OF GREASE-PROOFING CONTAINERS TO BE USED FOR THETRANSPORT OF LIQUID HYDROCARBONS, SUCH AS GASOLINE, OILS, LUBRICANTS ANDCONSISTING OF A SINGLE-LAYER POROUS PAPER HAVING A PH OF LESS THAN 6,THE STEPS OF APPLYING TO THE INSIDE WALL OF THE CONTAINERS A COATING OFAN AQUEOUS SOLUTION OF A LOW VISCOSITY GLUE AND OF A QUANTTY OFHEXAMETHYLENE TETRAMINE EQUAL TO ABOUT 0.2 TO 0.5 PER CENT OF THE DRYWEIGHT OF THE GLUE HEREUPON DIRECTLY FILLING THE CONTAINER WITH THELIQUID HYDROCARBON OF A SUFFICIENTLY LOW TEMPERATURE TO THEREBY CONGEALTHE COATING AND SEALING THE SAME WHEREUPON THE COATING IS HARDENED BYTHE FORMALDEHYDE SET FREE FROM THE HEXAMETHYLENE TETRAMINE BY CONTACTWITH THE ACID IN THE CONTAINER WALL AND DRIED BY COOPERATION OF ITSMOSITURE CONTENT THROUGH THE POROUS CONTAINER WALL.